DHS was vague about its plans, but the Center for Biological Diversity says the administration plans to build or replace 100 miles of fencing in Arizona and California, including through the two public lands. "The Trump administration just ignored bedrock environmental and public health laws to plow a disastrous border wall through protected, spectacular wildlands," the center's Laiken Jordahl tells AP.

Organ Pipe Cactus National Monument, established in 1937, encompasses 516 square miles filled with its unique namesake cactus. Cabeza Prieta National Wildlife Refuge, established in 1975 on land set aside in 1939, is home to 275 wildlife species. DHS, using redirected Pentagon funds, will replace waist-high bollard fences meant to stop vehicles with fences 18-30 feet high, AP reports. "The government will also build new roads and lighting in those areas in Arizona."

Organ Pipe Cactus was once a heavy corridor for drug smuggling, and much of the park was closed to visitors from 2002 to 2015, when "the National Park Service and Border Patrol conceived a plan to allow continued surveillance by the Patrol while Park Service crews erased hundreds of miles of illegal roads and road traces that had been woven through Organ Pipe Cactus," National Park Traveler reports. The waist-high fencing, put up in the mid-2000s, "succeeded in ending illegal vehicular border crossings while allowing wildlife to pass through." Environmental groups say the new fencing will further endanger vulnerable species, including jaguars and the Sonoran pronghorn.

The Defense Department said Friday that it intends to build 80 more miles of border fence using $1.5 billion taken from other projects, and on Sunday, The Washington Post revealed some details of where the Pentagon found its spare cash. Since Congress and Mexico have declined to fund President Trump's southern border wall, he has ordered the military to build it without congressional authorization, using authority claimed under a national emergency he declared and also by moving money around in the Pentagon's massive budget.

According to a Pentagon document obtained by the Post, this $1.5 billion will come from funds set aside to upgrade the Minuteman III intercontinental ballistic missile program and its aging ground control center; the Airborne Warning and Control System (AWACS) program and its reconnaissance aircraft, which provide airborne fighter jets surveillance and other information; an unidentified Defense Advanced Projects Research Agency (DARPA) "space test experiment"; funds to support coalition forces and the Afghan military; a military retirement fund; and other programs.

The Pentagon document doesn't detail how much money is being taken from each program, but The Associated Press reported Friday that $682 million will come from Afghan and coalition forces, $344 million from unspecified Air Force programs, $251 million from an ongoing program to destroy chemical weapons, and $224 from the military retirement system. In March, the Pentagon announced it's transferring $1 billion from military personnel funds for Trump's wall, and Trump plans to take another $3.6 billion in military construction funds.

The Pentagon said in the document obtained by the Post that it "carefully selected sources for the reprogramming that are excess or early to need and will not adversely affect military preparedness." Several top Democratic senators told the Pentagon on Friday that if it insists on flouting Congress' authority to dictate how federal money is spent, "we look forward to hearing your views on how you intend to repair the damaged relationship between the defense oversight committees and the department." Peter Weber

The most straightforward way to end President Trump's southern border emergency declaration is for Congress to terminate it with a joint resolution. The House is expected to easily pass such a resolution on Tuesday, giving the Senate 18 days to vote on the one-page, 80-word bill. On Monday night, Sen. Thom Tillis (R-N.C.) announced in a Washington Post op-ed that he will support the resolution, joining Sens. Susan Collins (R-Maine) and Lisa Murkowski (R-Alaska). Assuming all Democrats vote for the measure, it needs just one more Republican to pass in the Senate.

"Numerous Senate Republicans say that, like Tillis, they despise Trump's decision to declare a national emergency to get additional funding for his wall," Politico says. But based on interviews Monday with more than a dozen of those GOP senators, "most aren't ready to say they will vote to block him from doing so," which would carry a political cost. Trump urged Republicans to reject the resolution in a tweet on Monday, and there's little expectation Congress would override his threatened veto, "but significant Republican defections would give it momentum in the Senate and could raise the specter — however remote" — that Trump's emergency declaration will be killed by lawmakers, The New York Times reports.

At the least, Trump having to break out his veto pen "would be an embarrassing rebuke by a Congress opposed to his immigration agenda," and Republicans leaders are pressuring GOP lawmakers to support the president despite any reservations, Politico says. Democrats are encouraging GOP defections by pointing to the precedent Trump would be setting, citing letters from about 25 former GOP lawmakers and another from 58 ex-national security officials urging rejection of Trump's end-run around Congress, and circulating a list of military construction projects Trump might defund in each district to build his wall. "This isn't about the border," House Speaker Nancy Pelosi (D-Calif.) said Monday. "This is about the Constitution of the United States." Peter Weber

A bipartisan group of former national security officials is releasing an 11-page statement Monday arguing "there is no factual basis" for President Trump's declared national emergency to build his border wall. "Under no plausible assessment of the evidence is there a national emergency today that entitles the president to tap into funds appropriated for other purposes to build a wall at the southern border," write the 58 officials, including former Secretaries of State Madeline Albright and John Kerry, former Defense Secretaries Chuck Hagel and Leon Panetta, and several other officials from previous Republican and Democratic administrations.

The statement cites federal statistics and reports to show that contrary to Trump's claims, border crossings are near 40-year lows, there are no documented terrorism or crime emergencies near the U.S. border, a wall wouldn't significantly reduce drug trafficking, and "a wall is unnecessary to support the use of the armed forces." Released one day before the House will vote to terminate Trump's emergency order, the document is partly intended to bolster legal challenges to the declaration. Federal courts cited a statement signed by several of the same former officials when blocking Trump's original Muslim travel ban in early 2017; a significantly revised and narrowed ban was later upheld by a 5-4 Supreme Court. Peter Weber

Homeland Security Secretary John Kelly has commissioned a study on the costs to build President Trump's border wall with Mexico, Reuters reports, and the group has already come up with a ballpark figure for building fences and walls along the entire border: $21.6 billion. That's significantly higher than the $12 billion Trump estimated in his campaign, and the approximately $15 billion touted by House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell. Trump says U.S. taxpayers will foot the bill and Mexico will reimburse America; Mexico has no plans to do so.

The report, which Reuters saw on Thursday, has not yet been presented to Kelly, and the Trump administration may not follow its recommendations. Its price tag is closer to the $25 billion cost estimate from investment research group Bernstein Research.

The Trump White House has already started planning to build the wall, with the expectation that Congress will approve funding in April or May. DHS has reportedly begun seeking environmental waivers to build in some sensitive parts of the border, worked up steel orders, and reached out to existing contractors. The report envisions three phases, starting with a $360 million section near San Diego, El Paso, and in the Rio Grande Valley of Texas. The next phase would tackle 151 miles around the Rio Grande Valley, Laredo, Big Bend National Park, and Tucson; and the final phase would cover the last 1,080 miles of border. The wall would be finished by 2020, according to the plan.

Along with the costs of materials, road building, and labor, the government would have to expend millions using eminent domain to acquire private land along the border, and some areas would present costly geographical challenges. Peter Weber

Texas sends 38 lawmakers to Congress — 36 House members and two senators — and 25 of them are Republican. None of them are willing to endorse President Trump's plan for a gulf-to-sea border wall. Not all of Texas' congressional delegation necessarily opposes the wall, but when The Texas Tribune asked about Trump's signature policy issue a few weeks ago, none would go on record as thinking it is a good idea.

Many of them were in favor of erecting barriers in some sections of the border, adding Border Patrol officers, and using surveillance technology, but Sens. John Cornyn (R) and Ted Cruz (R) only backed completing the last 50 miles of 700 miles of border fencing approved by Congress in 2006, most of it in Arizona. Others fretted about using eminent domain to seize land from ranchers, often family land passed down for generations.

Rep. Will Hurd (R), whose competitive House district spans 800 miles of border, from San Antonio to right outside El Paso, released a stronger statement on Wednesday. "Building a wall is the most expensive and least effective way to secure the border," he said. "Big Bend National Park and many areas in my district are perfect examples of where a wall is unnecessary and would negatively impact the environment, private property rights, and economy," Hurd said, adding that it would be "impossible" to build a wall in some sections of his district. Peter Weber

When President Trump signed his executive order on Wednesday to start construction on his border wall along the U.S.-Mexico border, one of the big questions was where the money will come from. Trump has long promised he will somehow get Mexico to pay for building the wall, though he has recently switched to promising Mexico will reimburse U.S. taxpayers. Mexican President Enrique Peña Nieto reiterated on Wednesday that Mexico will do no such thing. On MSNBC Wednesday evening, House Speaker Paul Ryan said taxpayers will foot the bill, at least for now, and agreed it will cost them billions.

"Well, first off, we're going to pay for it and front the money up," he told Greta Van Susteren. "There are a lot of different ways of getting Mexico to contribute to doing this, and there are different ways to defining how exactly they pay for it. Point is, he has a promise he made to the American people, which is to secure our border — a wall is a big part of that. We agree with that goal, and we will be working with him to finance construction of the physical barrier, including the wall, on the southern border."

"The law is already on the books — I voted for it like 10 years ago — but nothing has gotten done, and now we have a president who actually wants to secure the border," Ryan said. "I think a lot of people want to secure the border, on both sides of the aisles," Van Susteren said, "but the estimates are $8 billion to $14 billion..." "That's about right," Ryan agreed.